Winery Cellar Floor Moisture: How to Test a Slab Before You Coat It

By Pablo Figueroa · October 26, 2026 · 4 min read

A cellar slab sits in a cool, damp room and gets washed on a schedule. That is a hard place for a coating to bond, and the moisture in the slab decides a lot of it. This guide covers how slab moisture is tested, why the conditions of the test matter, and what to do with the number.

Why does slab moisture matter under a coating?

A coating bonds to the concrete under it. Moisture moving up through the slab can push on that bond from below. LATICRETE, a resinous flooring manufacturer, describes high slab moisture and moisture vapor transmission as "one of the leading causes of resinous flooring issues and failures." Testing before the system is chosen is how that risk gets priced instead of discovered.

How is slab moisture tested?

The common method for relative humidity is ASTM F2170, which uses probes set into holes drilled in the slab. Wagner Meters’ published summary gives the main requirements below. ASTM currently lists F2170-19a as active; use the specified edition and equipment instructions for the actual test. This overview does not replace the full standard:

• Hole depth is 40 percent of slab thickness when the slab dries from one side, and 20 percent when it dries from two. A 6-inch slab on grade means a 2.4-inch hole.
• The test needs three holes for the first 1,000 square feet and at least one more for each additional 1,000.
• The slab and the air above it must be at service conditions for at least 48 hours before testing.
• The hole is sealed and left to reach equilibrium before the first documented reading. Wagner’s guidance specifies at least 24 hours, reduced from the older 72-hour requirement. Name the standard edition in the specification and follow its procedure.

Why does the room matter?

Because of the 48-hour rule. A barrel room is typically kept cool and humid. Building Science Corporation describes traditional French cellars at about 55°F and 80 to 90 percent relative humidity for barrels. Those are examples, not universal operating targets; use the actual facility’s intended conditions. A test taken in a warm, dry room during a build can give a different reading than the room will give in use. Test where the floor will live.

What number is acceptable?

The test does not decide that. The coating manufacturer sets the limit for each system. As one example, LATICRETE’s SPARTACOTE guidance recommends a moisture vapor barrier primer when relative humidity in the concrete measures 75 percent or greater. That is product-family guidance, not a universal pass/fail limit for all coatings. A different system can carry a different limit, so ask for the number in writing for the exact product on the quote.

What if the slab reads high?

The specified floor coating system may need a compatible moisture mitigation layer or a different system. A mitigation layer has its own cure time before the next coat can go on. LATICRETE’s comparison lists recoat times as short as 3–4 hours for one product and 12–72 hours for another. These are product-specific examples, not a promised return-to-service time; confirm the current data sheet, temperature requirements and recoat window for the exact system. Build that time into the off-season schedule before the slab is tested, not after.

Do all rooms need their own test?

Yes. A winery that grew in stages can have slabs of different ages, thicknesses and ground beneath them. Assess and include each room in the test plan, with locations and test counts based on slab area, construction and potential high-moisture zones. ASTM notes that results describe only the locations and time tested. DTI’s zone-by-zone floor assessment guide explains how this fits into the wider review of winery flooring.

What does the full picture look like?

The Floor Front, our LinkedIn newsletter, covers the cellar floor in depth, including the spec checklist and the cost comparison between a tested slab and an assumed one.

Planning cellar floor work? Request a free floor-condition assessment or call (209) 879-9674.

Image: AI-generated illustration of slab moisture testing in a winery cellar, not a documented DTI project.